The venoms of the rattlesnakes Crotalus cerastes cerastes, C. ruber ruber, C. adamanteus and C. molossus will be characterized for their biologically active peptides and certain proteins, using gel filtration, ion exchange chromatography, gel electrophoresis, dialysis, ultrafiltration, ultracentrifugation, and ammonium sulfate precipitation. Further chemical characterization, including amino acid analysis and sequencing, will be carried out. The biologically active fractions will be studied, using several acute and chronic central nervous system preparations, the Bulbring nerve-muscle and crayfish DEAM preparations, neuroblastoma culture cells, tissue cultures, cardiovascular survey preparations, the rabbit ear artery-nerve preparation, vascular preparations and techniques adapted for determining the hemorrhagic and necrotizing properties of the fractions. The data will be organized for potential use in developing an immunizing mixture of certain of the venom components for subsequent research and clinical trial. The value of the peptides medicine and as biological tools will be pursued.